1. Lacking worldly experience and understanding, especially:
   1. Simple and guileless; artless: a child with a naive charm.
   2. Unsuspecting or credulous: "Students, often bright but naive, bet—and lose—substantial sums of money on sporting events" (Tim Layden).
   3. Not previously subjected to experiments: testing naive mice.
   4. Not having previously taken or received a particular drug: persons naive to marijuana.
2. Showing or characterized by a lack of sophistication and critical judgment: "this extravagance of metaphors, with its naive bombast" (H.L. Mencken).
3. 1. Not previously subjected to experiments: testing naive mice.
   2. Not having previously taken or received a particular drug: persons naive to marijuana.

Synonyms: These adjectives mean free from guile, cunning, or sham. Naive sometimes connotes a credulity that impedes effective functioning in a practical world: "this naive simple creature, with his straightforward and friendly eyes so eager to believe appearances" (Arnold Bennett).
Simple stresses absence of complexity, artifice, pretentiousness, or dissimulation: "Those of highest worth and breeding are most simple in manner and attire" (Francis Parkman). "Among simple people she had the reputation of being a prodigy of information" (Harriet Beecher Stowe).
Ingenuous denotes childlike directness, simplicity, and innocence; it connotes an inability to mask one's feelings: an ingenuous admission of responsibility.
Unsophisticated indicates absence of worldliness: the astonishment of unsophisticated tourists at the tall buildings.
Natural stresses spontaneity that is the result of freedom from self-consciousness or inhibitions: "When Kavanagh was present, Alice was happy, but embarrassed; Cecelia, joyous and natural" (Henry Wadsworth Longfellow).
Unaffected implies sincerity and lack of affectation: "With men he can be rational and unaffected, but when he has ladies to please, every feature works" (Jane Austen).
Guileless signifies absence of insidious or treacherous cunning: a guileless, disarming look.
Artless stresses absence of plan or purpose and suggests unconcern for or lack of awareness of the reaction produced in others: a child of artless grace and simple goodness.